This invention relates in general to the field of continuous casting and forming of metal rods and more particularly, to an apparatus and method for cutting such rods while they are moving at high speeds between apparatus such as a rolling mill and apparatus such as a coiler. Cutting a rapidly moving rod of metal has been difficult to achieve in the prior art because if the shear blades interrupt the continuous passage of the rod, or if they otherwise retard the speed of the portion of the rod moving toward the blades, the rod will buckle and form a cobble or will be deflected from its proper linear path.
One approach to nondisruptive cutting of rapidly moving metal rod involves the use of a rotary shear. Under this approach, a pair of guide wheels each having a groove around the peripheral surface thereof are mounted on parallel shafts and interconnected by gear means so that their rotation is synchronous but in opposite directions. The wheels and shafts are mounted so that the grooves in the peripheral surfaces are adjacent and form a passageway through which the rapidly moving rod is passed. A pair of blades, one rotatable with each wheel, are selectively inserted through the wheels into the passageway formed between the wheels in order to fill the entire passageway and thereby sever the rod.
In the prior art, the blades have been slid into and out of cutting position in the peripheral grooves of the guide wheels by mechanically connecting them to the piston rod of a pneumatic cylinder. The pneumatic cylinder is controlled by a pair of solenoid valves, each of which direct compressed air to one of the ends of the cylinder, thereby causing the piston to move either in or out.
This prior art rotary shear has proved adequate for waste or "cobble" cutting of rod since such cutting involves repetitive cutting of the rod to remove the waste or cobble and since it is normally not critical that cobble cutting start or stop at a given moment or at a given point on the rod. It has also proved adequate for cutting relatively slowly moving rod with a single cut to obtain rod of a particular length. However, serious problems arise when a prior art rotary shear is used to make a single cut of a rod moving at those linear speeds typically achieved by high production continuous casting and rolling apparatus.
For example, in a high production continuous casting and rolling apparatus for rod, the rod moves from a rolling mill or other hot forming apparatus at linear speeds of between 2600-3000 feet per minute and it has been a practical impossibility in the prior art to insert and withdraw cutting blades with solenoid valves and a pneumatic cylinder within the time required for one revolution of the guide wheels unless the guide wheels are of such diameter as to be impractical. This is because at such a speed, one revolution of guide wheels of such diameter as to be practical requires approximately 50 milliseconds, whereas the fastest available solenoid valves and pneumatic cylinders have a combined response time of about 50 to 60 milliseconds.
If the cutting blades are not withdrawn from cutting position within the passageway formed by the guide wheels within one revolution of the guide wheels following the first cut of the rod by the cutting blades, the rod will be cut a second time, nicked by a partially withdrawn blade, or otherwise damaged and made unsuitable for drawing into wire. Moreover, multiple cuts result in waste portions of rod which must be removed before they foul a component of the continuous casting and rolling apparatus, such as a coiler, downstream of the shear.
A further problem with prior art rotary shear is that if the cutting process is begun by a manual pushbutton, the pushbutton might commonly be held in for as long as 1/2 second, a period of time long enough to start the cutting process a second time considering the short period of time in which insertion of the blades, cutting, and withdrawal of the blades must be accomplished. Moreover, another problem with prior art rotary shears if a manual pushbutton is used is that it is clearly impossible to use a manual pushbutton to signal the insertion of the blades, wait until the rod is cut, and then signal the withdrawal of the blades and still accomplish withdrawal of the blades before the blades make another revolution with the guide wheels and a second cut of the rod.
Attempts have been made in the prior art to solve the problem described above by beginning withdrawal of the blades before the rod is cut with an automatic timing device responsive to the position of the blades. The aim of this approach is to cut the rod while the withdrawal solenoid valve is building up enough magnetic field to positively open the valve and move the piston of the pneumatic cylinder. However, automatic timing devices have also encountered problems because the response time of the solenoid valves alone is significant compared to the period of revolution of guide wheels of a practical size used with rod moving at typical speeds.
This is because such an automatic timing system must not cancel the signal to the "blade-in" solenoid and start a signal to the "blade-out" solenoid before the "blade-in" solenoid has built up enough magnetic field to positively open the valve and thereby move the cylinder piston and insert the blades. If the timing system starts withdrawal too early, no cut will be made. On the other hand, if such withdrawal is begun too late, either a second cut will be made in the rod or the rod may be nicked and made unsuitable for drawing into fine wire.
Attempts have been made to solve this problem of timing encountered by automatic timing devices by connecting the solenoid valves to two vane switches which are triggered by vanes rotating with the guide wheels. However, over a range of high speeds, this apparatus has proved unable to consistently initiate withdrawal of the cutting blades within the required critical interval of time.